1. Field of the Invention
The field of this invention is earth boring bits--especially the seal and lubrication systems for rolling cutter rock bits.
2. Background Information
Recently, a meal face seal has been used successfully to seal lubricant within the rotatable cutter and around the cantilevered bearing shaft of a rock bit. U.S. Pat. No. 4,516,641, "Earth Boring Bit With Pressure Compensating Rigid Face Seal", May 14, 1985, includes background information leading to this important milestone in the continuing search for seal improvement. The seal disclosed in the '641 patent utilizes two rigid face seals which are urged against one another by a pair of O-ring type elastomeric seals confined in a seal groove between each cutter and its supporting bearing shaft. Since axial seal assembly movement is greater than axial cutter movement, seal and groove geometry is provided to permit unrestricted seal assembly movement. As a result, pressure pulses in the lubricant around the seal and lubricant losses are minimized. The seal assembly becomes a supplemental pressure compensator that assists the primary pressure compensator in each leg of the bit in maintaining a selected static, low pressure differential across the seal assembly.
An improvement to the structure disclosed in the '641 patent is disclosed in U.S. Pat. No. 4,666,001, "EARTH BORING BIT WITH IMPROVED RIGID FACE SEAL ASSEMBLY", May 19, 1987. Here, the positioning of the seal groove and seal assembly in relation to the journal bearing surface is such that rigid ring movement is decreased relative to axial cutter movement. In the preferred embodiment of the '001 patent the ratio of rigid ring movement to axial cutter movement is substantially one half to one. Hence, prolonged life of the seal assembly may be expected.
Each of the seal assemblies disclosed in the above patents uses two opposed rigid face rings and two resilient energizer rings in a groove configuration to achieve lubricant pressure equalization in the vicinity of the seal. In the related copending application which is now U.S. Pat. No. 4,753,303 is disclosed a seal assembly with fewer components in a reduced space. The volume and pressure of the lubricant adjacent the seal is essentially balanced. This also simplifies manufacture, forseeably reduces costs, and enables utilization to a wider variety of bit sizes and bit types.